This invention relates to a transparent shock-absorbing laminate and a flat panel display using the same. More particularly, it relates to a shatterproof and fracture-proof shock-absorbing laminate which is to be formed on a glass substrate of a flat panel display, especially a glass substrate of a plasma display panel.
Glass cathode-ray tubes (CRT) for TV sets and other displays are required to be shatterproof and not to allow a falling steel ball to pierce and make a hole of finger size or greater (which may give an electric shock) in a falling ball test as regulated by safety standards (e.g., UL Standards and Electrical Appliance and Material Control Law, Japan) To meet these standards the CRT glass panel should have some thickness.
In order to achieve weight reduction while securing shatterproofness, CRT glass panels laminated with a self-repairing synthetic resin protective film (preferably a thermosetting urethane resin film) have been proposed in JP-A-6-333515 and JP-A-6-333517. These glass panels are characterized by their shatterproofness but are not protected against breakage.
Flat panel displays (hereinafter FPDs) include field emission displays (FEDs) , plasma addressed liquid crystal (PALC) displays, liquid crystal displays (LCDs), and plasma display panels (PDPs). PDPs have been attracting attention for their widescreen, but the glass substrate used in PDPs are particularly thin and fragile.
JP-A-11-174206 discloses a transparent resin sheet as a protective filter for protecting the inner glass substrate of FPDs such as LCDs or PDPs. The protective filter is set within 10 mm apart from the front surface of the display. Because of the space between the glass panel and the protective filter, there are left many problems, such as double reflection of external light, an increase of reflectance, and reduction in image sharpness due to parallax. Further, dust or stain (e.g., nicotine) will be accumulated in the space which is difficult to clean.
PDPs, which have ever been required to have a wider display area and a smaller weight, have shown a tendency to have a reduced thickness. It produces a contrary effect to put a protective filter in front of the panel. There has not been developed a thin and light protective filter against breakage for a PDP of large size.
PDPs comprise an array of cells containing a rare gas, particularly a neon-based gas, in which a discharge is generated to produce vacuum ultraviolet rays, by which phosphors (R, G and B) provided in the cells are excited to emit fluorescence. In this emission process, electromagnetic waves and near infrared rays which are unnecessary for the mechanism of a PDP are also emitted. Electromagnetic wave emission, in particular, is regulated by FCC regulations, VCCI (Voluntary Council for Interference by Information Technology Equipment, Japan) guidelines, etc. In recent years, harm of electromagnetic waves to human bodies is of concern. It is therefore necessary to shield the electromagnetic waves emitted from PDPs.
The near infrared (NIR) rays emitted from PDPs have wavelengths of about 800 to 1200 nm. The IR radiation can interfere with remote controls of electric appliances, karaoke equipment, audio and visual equipment, etc. which typically operate in a wavelength region of from about 700 to 1300 nm. Therefore, it is also necessary to cut the NIR rays emitted from PDPs.
Under these circumstances, a filter for cutting electromagnetic waves and IR rays emitted from PDPs has been demanded. Filters that have been heretofore proposed include a filter having a metal mesh embedded therein, an acrylic resin plate having an etched mesh pattern, an acrylic resin plate containing an NIR-absorbing dye, and a transparent multilayer laminate having a thin metal film sandwiched in between transparent thin films.
Application of these filters to PDPs has been studied. A filter used for such a display as a PDP usually comprises a glass substrate or an acrylic resin substrate which is not placed in contact with a PDP via a transparent adhesive layer but is within 10 mm apart from the front surface of a PDP. If it is adhered directly to a PDP, there is a fear that the glass substrate of a PDP may be fractured.
One object of the present invention is to provide a transparent shock-absorbing laminate having shatterproofness and fracture-proofness, which is adhered directly to a PDP glass substrate via a transparent pressure-sensitive adhesive, and a display comprising the structure.
Another object of the present invention is to provide a transparent shock-absorbing laminate having electromagnetic and/or NIR shielding properties as well as shatterproofness and fracture-proofness, which is adhered directly to a PDP glass substrate via a pressure-sensitive adhesive, a display comprising the structure.
The objects of the present invention are accomplished by:
a transparent shock-absorbing laminate to be formed on a glass substrate for a display panel having a fracture strength such that it is fractured by a falling ball impact (drop height: 1.5 m; ball weight: 510 g) corresponding to 79,000 N, said transparent shock-absorbing laminate comprising a shatterproof layer having a shearing modulus of 2xc3x97108 Pa or more, at least two fracture-proof layers having a shearing modulus ranging from 1xc3x97104 to 2xc3x97108 Pa, each having different modulus, and a transparent pressure-sensitive adhesive layer; and
a flat panel display, such as a PDP, which comprises the above-described transparent shock-absorbing laminate adhered on a glass panel substrate thereof.
In a highly preferred embodiment of the invention, the shock-absorbing laminate further comprises a transparent electromagnetic shielding layer and/or an NIR shielding layer having a transmission of 20% or less in a wavelength region or from 800 to 1200 nm.
The shock-absorbing laminate preferably has a thickness of 2 mm or smaller and a visible light transmission of 40% or higher, whether or not it has the electromagnetic shielding layer and/or the NIR shielding layer.
The transparent shock-absorbing laminate preferably absorbs 50% or more of a falling ball impact which corresponds to an impact force of 79,000 N.
In another highly preferred embodiment, the transparent shock-absorbing laminate has a layer order of shatterproof layer (1)/fracture-proof layer (2)/fracture-proof layer (3)/ . . . fracture-proof layer (n)/pressure-sensitive adhesive layer (n+1), and the shearing moduli of the fracture-proof layers (2) to (n) are such that the absolute logarithmic values of shearing modulus (G) ratios of upper to lower layers adjacent to each other via every interface among the layers (1) to (n+1) (hereinafter referred to as G ratios) are added up to give the greatest sum, the sum of G ratios being represented by:
|Log G1/G2|+|Log G2/G3|+ . . . +|Log Gnxe2x88x921/Gn|+|Log Gn/Gn+1|.
In still another preferred embodiment, the shock-absorbing laminate basically comprises the pressure-sensitive adhesive layer, the fracture-proof layer, the shatterproof layer and an antireflective layer in this order, and further comprises an electromagnetic shielding layer and/or an NTR shielding layer.
Because the shock-absorbing laminate is directly bonded to a glass substrate or a PDP, etc., inconveniences due to an air gap (reduction in image sharpness, double reflection of external light, accumulation of dirt, staining with nicotine) can be eliminated. The transparent shock-absorbing laminate of the invention which has an electromagnetic shielding layer and/or an NIR shielding layer exhibits excellent shielding performance in addition to the above characteristics.